In Marcia's First Tennis Lesson, Her Instructor Keith Is Trying

In Marcia's first tennis lesson, her instructor Keith is trying to teach her the correct way to swing a tennis racket. Keith praises Marcia every time she hits the tennis ball over the net and into the "in bounds" area of the opponent's side of the court using the correct body position. Marcia shows little improvement during the one-hour lesson. From a behaviorist perspective, what mistake is Keith probably making in teaching Marcia to play tennis?

A) He fails to realize that Marcia has little to gain by changing her behavior.
B) He is using intermittent rather than continuous reinforcement.
C) He should shape the behavior rather than expect immediate mastery.
D) Praise is rarely an effective reinforcer.